A common arrangement in many industrial processes includes a machine having an endless looping belt upon which the belt surface is cleaned or subjected to fluid spray, such as in the cleaning and re-conditioning of felt fabric belts in paper making machinery. It will be understood however, that the present invention is not restricted to any type of machinery, but can have application to any such process machinery.
In the paper making process, a felt fabric belt is used to absorb water from newly manufactured paper webs. Periodic cleaning of the fabric belt surface is required to remove fibers, fillers, pitch or other particles which would otherwise adhere to the belt surface, impair the paper finish and impede operation of the paper making machine. In order to clean the surface of these contaminants, fluid nozzles are commonly directed at the surface at an angle between 10 and 45 degrees to chisel or skive the surface with jet energy.
In general, very little engineering effort has gone into optimizing the design of such cleaning nozzles. The velocity of the stream of fluid and the angular orientation to the moving belt are generally determined through trial and error or by experience of the machine builders.
However, particularly in the case of a felt fabric belt, the surface can be damaged significantly by improper orientation of fluid streams. If the nozzle angle is excessively acute relative to the belt, the belt surface may be damaged by raising and shredding the surface fibers of the felt.
In the case of fabric felt belts, absorbed penetrating water is required to supply energy within the felt to re-open and restore the compressed caliper in the press nip. During passage through the paper making machine, the felt fabric belt is repeatedly dried and then pressed against a wet paper web to absorb water from the paper web. The fabric belt is under tension as it passes over rollers and is compressed as the belt rides over and between rollers. Compaction of the fabric reduces its absorption capacity and increases the resistance to water removal from it by suction devices.
To ensure that proper operation of the felt fabric belt, it is necessary to re-open the voids between fibers and restore the compressed thickness of the belt. A felt fabric belt which is highly compressed with compact fibers has reduced capacity to absorb water from the paper web and requires excessive de-watering effort must be replaced with a new fabric belt.
Injecting water under pressure to the interior of the felt fabric, designers of paper making machinery attempt to re-open and restore the compressed caliper of the felt fabric belt by expanding the thickness of the belt, separating fibers to restore the porosity and void ratio of the belt.
Conventionally, in order to restore the compressed caliper, a separate shower arrangement is provided that directs fluid streams at the belt normal to the belt surface and transverse to the belt direction.
A significant disadvantage of such prior art devices is that the optimum use of fluid and optimum angle of impact is not achieved since heretofore, the design of nozzles and their angular orientation relative to the belt has been decided on the basis of trial and error, or experience with similar applications. Excessive fluid is used when an optimum impact angle is not used since fluid merely splashes off the belt surface without doing useful work and possibly damaging the belt surface.
The present inventor however, has recognized that the belt velocity has significant effect upon the optimum velocity and optimum angular orientation of the nozzle stream of fluid.
It is an object of the present invention to provide a shower with nozzles which can be utilized for both functions of cleaning the belt surface and penetrating the belt itself to restore the compressed caliper.
It is a further object of the invention to provide an impact angle changing shower which can be adapted to compensate for the variation in impact velocity and impact angle caused by the belt velocity.
It is a further object of the invention to provide an actuating mechanism which can rotate the nozzles about a horizontal axis and which can selectively oscillate the nozzles axially transverse to the belt direction in order to provide complete uniform coverage of the entire belt surface.